In an exchange (hereinafter, referred to as a “unit”), the parameter or the like of the unit is sometimes set according to a recommended standard 232 version C (RS232-C) serial interface complying with the RS232-C. Further, there is a structure in which a printer having the RS232-C serial interface is connected to the unit.
Constructing such a unit as a duplexed unit including an operation system unit and a standby system unit sometimes increases the reliability. In the duplexed unit, when a malfunction occurs in the operation system unit, the standby system unit is newly used as the operation system unit. At that time the printer that has been connected to the operation system unit according to the RS232-C serial interface needs to be connected to the standby system unit without a human operation.
Patent Literature 1 describes a technique in which an operation system switch is provided with a first data converting part and the like, a backup system switch is provided with a second data converting part and the like, and the first data converting part and the second data converting part are bi-directionally connected to each other through a first transfer line, a second transfer line, and a third transfer line. The first transfer line bi-directionally transfers serial data. The second transfer line bi-directionally transfers a clock. The third transfer line bi-directionally transfers a frame pulse.
Patent Literature 2 describes a technique in which a data transfer device on the transmitting side performs a parallel/serial conversion by combining a parallel status control signal with a parallel data signal in order to convert the signals into a serial signal. The serial signal, a clock signal, and a synchronization signal are transmitted to a data transfer device on the receiving side.